1. Field of the Invention
The present invention relates to an audio visual information signal reproducing apparatus for reproducing an audio visual information signal of the MUSE (Multiple Sub-Nyquist Sampling Encode) system, which is a transmission system for high definition television in Japan, and particularly relates to a video disc player of the MUSE system for preventing a noise from being generated when audio reproduction is abruptly interrupted.
2. Description of the Prior Art
Video disc players which reproduce video signals of the MUSE system from optical discs are being developed. In the MUSE system, a wide band high definition TV signal is compressed by approximately 1/4 times and then transmitted. Moreover, in the MUSE system, an audio signal is digitized, compressed, and encoded. The resultant signal is time-division multiplexed in a vertical blanking interval of a video signal. Thus, high quality sound suitable for the high quality video can be reproduced.
FIG. 1 is a block diagram showing the construction of a conventional video disc reproducing system. In FIG. 1, a reference numeral 501 denotes a video disc player of the MUSE system for reproducing a video disc on which a MUSE signal is recorded. This video disc player 501 is hereinafter referred to as the MUSE video disc player. The MUSE video disc player 501 reproduces a MUSE signal from a MUSE video disc. The reproduced MUSE signal is supplied to a MUSE decoder 502. The MUSE decoder 502 decodes the MUSE signal into a video signal and an audio signal. The video signal reproduced from the MUSE decoder 502 is supplied to a display 503 with an aspect ratio of 16 to 9. Thus, a high definition TV picture is reproduced on the display 503. On the other hand, the reproduced audio signal is supplied to an audio amplifier 504. The audio amplifier 504 amplifies the reproduced audio signal and sends the signal to a speaker 505. The speaker 505 outputs the reproduced audio signal.
In the conventional MUSE video disc player system, when the reproduction is completed, when the power is turned off, or when a special play mode is performed, the speaker generates an uncomfortable noise. This is because in the MUSE system compression and encoding based on DPCM (Differential Pulse Code Modulation) are performed. Thus, when the reproduction is abruptly interrupted, audio data becomes in error.
In other words, even a small error of a digital audio signal adversely affects a decoded analog output, resulting in a large noise. Thus, generally, a digital audio signal is encoded with an error correction code having high error correction capability. A MUSE audio signal is encoded with an error correction code at intervals of an audio frame which is equivalent to data for 1 msec. Thus, even if an error takes place, when it is within the correction capability, it is corrected. However, if a MUSE signal which is supplied to the decoder abruptly stops, an error which exceeds the error correction capability takes place. Thus, when the reproduction is completed, an uncomfortable noise takes place.
To solve this problem, as shown in FIG. 1, a control line 506 is disposed between the MUSE video disc player 501 and the MUSE decoder 502. When the reproduction of the MUSE video disc player 501 is stopped, the MUSE video disc player 501 sends a mute command to the MUSE decoder 502 so as to mute the audio reproduction.
However, when the control line 506 is provided, the number of control lines increases. Moreover, connecting the MUSE video disc player 501 and the MUSE decoder 502 with the control line 506 is non-standard. Thus, the MUSE video disc player 501 may not be used with MUSE decoders requiring the control line 506.
In addition, as shown in FIG. 2, another apparatus has been proposed where a switch 507 is disposed in the MUSE video disc player 501 so as to supply the audio output of the MUSE decoder 502 to the audio amplifier 504 through the switch 507. In the normal reproduction state, the switch 507 is turned on. Then, just before the reproduction of the MUSE video disc player 501 is interrupted, the switch 507 is turned off.
As shown in FIG. 2, when the switch 507 is provided in the MUSE video disc player 501, it is not necessary to provide the control line between the MUSE video disc player 501 and the MUSE decoder 502.
However, in this case, it is necessary to provide an audio signal line 508 between the MUSE decoder 502 and the MUSE video disc player 501, which is again non-standard.